1. Beyond Mendel

2. Mendelian Heredity What did Mendel say about Heredity?
Alternate versions of genes
One allele from each parent
Dominant and recessive alleles
Most traits are not inherited in the simple patterns identified by Mendel (single allele trait)
Not all genes have only 2 alleles
Not all traits are controlled by one gene
In nature, other patterns exist

3. Polygenic Inheritance
When several genes affect a trait
Children may have blended traits of both parents
Examples
Eye color
Skin color
Height

4. Incomplete Dominance
A form of intermediate inheritance in which heterozygous alleles are both expressed, resulting in a combined phenotype.
Neither allele is completely dominant over another
Example:
If a snapdragon with red flowers is crossed with a snapdragon with white flowers, the offspring will have pink flowers

5. Multiple Alleles
Traits that can be determined by 3 or more possible alleles
Still, only two alleles for a gene can be present in one individual
Three or more alleles – or types of genes – can be passed on, but only 2 will be passed on

6. Multiple Alleles, an Example:
A human’s blood type is determined by 2 of three possible alleles
IA, IB, & i
Different combinations of these three alleles can produce four different blood types
A, B, AB & O
Genotype
Phenotype (Blood Group)
IAIA A
IAi
IBIB B
IBi
IAIB AB ii O

7. Codominance
A condition in which two traits can appear at the same time, both fully expressed
Example:
Roan Fur on Cattle
If red furred cattle are crossed with white furred cattle, the offspring will have red and white fur
DAD
MOM
OFFSPRING + =

8. Sex-Linked Traits X* X X*X XX Y X*Y XY
When a gene is located on either an X or Y chromosome
Most are X linked because the X chromosome is longer than the Y chromosome
Example:
Color Blindness is linked on the X chromosome